Method for Manufacturing Ceramic Honeycombs

Abstract

Methods for making extruded ceramic products meeting set dimensional specifications comprise subjecting a small firing sample taken from a first unfired product preform to a rapid firing treatment to determine a value for firing shrinkage or growth, and then adjusting the dimensions of succeeding unfired preforms based on that value, e.g., by adjusting wet extruded product dimensions, so that the succeeding preforms will meet the set dimensional specifications.

Description

CROSS-REFERENCE To RELATED APPLICATIONS[0001]This application claims the benefit of priority to U.S. provisional application No. 61 / 092,260, filed on Aug. 27, 2008.BACKGROUND[0002]1. Field of Invention[0003]The present invention is in the field of ceramic honeycomb manufacture, and more particularly relates to methods for manufacturing ceramic honeycomb products that provide improved product selection rates and thus reduced manufacturing costs.[0004]2. Technical Background[0005]Ceramic honeycombs useful as catalyst supports and filter substrates for the removal of pollutants from combustion engine exhaust gases are well known. Such honeycombs comprise a plurality of parallel channels or cells bounded by thin intersecting ceramic walls or webs, all channels lying parallel to a common channel axis. Honeycombs of rounded prismatic or cylindrical shape, having cross-sections of circular, oval, elliptical, or “racetrack” shape transverse to the common channel axis, are common. The cerami...

AI Technical Summary

Benefits of technology

[0011]The present invention provides a rapid method for collecting firing shrinkage / growth information from dried honeycomb shapes. The method thus permits timely compensating adjustments to be made to the dimensions of wet extruded honeycomb shapes early in a production run, in order that the dried ware thereafter produced will meet the final required dimensional tolerances when fired. As an example of the benefit of the method, the invention reduces the time required to determine firing dimensional changes from a standard firing cycle for the dried honeycomb shape, e.g., 10-14 days for some honeycomb compositions, to one-half of the standard firing cycle or less, e.g., not exceeding 120 hours, or not exceeding 24 hours in some cases. The result is a considerable improvement in overall product selection rates and a corresponding reduction in filter production costs.

Problems solved by technology

Current processes for the large-scale manufacture of porous ceramic honeycomb substrates useful in the construction of wall-flow particulate filters for the removal of particulates and other pollutants from combustion engine exhaust gases are complex and expensive.

The high costs of honeycomb manufacture require that product selection rates for the honeycombs be as high as possible.

Fired honeycomb products that do not have sizes or contours meeting these dimensional tolerances are not saleable and must be scrapped or recycled at considerable additional expense.

Control is complicated by the fact that firing shrinkage (or growth) is variable and subject to change as the result of raw material variability, batch processing inconsistencies, and other factors.

Achieving effective firing shrinkage or growth compensation through control of extruded shape is further complicated by the fact that the firing cycles required to achieve high fired honeycomb yields are extremely long.

Long firing cycles mean that the time required to receive firing shrinkage feedback for ware in process is prohibitively long.

Several days of production can be at significant risk of being out of dimensional tolerance, and significant fractions thereof can be lost in the event that unanticipated firing shrinkage or growth causes the final dimensions of some of that production to be out of customer contour specifications.

Raw materials costs for the latter filters are relatively high, the firing cycles needed to produce defect-free honeycombs are particularly long, and consistently meeting customer contour specifications for the finished filters requires particularly close attention to firing shrinkage variations.

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